THE EFFECT OF REDUCED GROWTH AREA BY SUBSTRATE PATTERNING ON MISFIT ACCOMMODATION IN MOLECULAR-BEAM EPITAXIALLY GROWN INXGA1-XAS/GAAS

The effect of reduced growth area on the misfit accommodations of In(x)Ga(1-x)As/GaAs grown by molecular beam epitaxy has been studied with cross-sectional transmission electron microscopy (XTEM). Composition grading techniques as well as strained-layer superlattices were used for In(x)Ga(1-x)As composition up to x = 0.53 and growth areas which ranged from approximately 10 cm2 (blanket areas) to 4-mu-m squares. Results indicate that the use of step-composition grading and linear-composition grading are particularly effective when combined with reduced growth areas up to 30 X 30 mu-m and In(x)Ga(1-x)As compositions up to x = 0.25. Dislocations which are generated for misfit accommodation during growth are effectively driven to the edges of the patterned growth areas with considerably fewer interactions than dislocations nucleated in blanket areas. XTEM samples prepared from blanket areas were generally found to contain randomly distributed threading dislocation-free regions on the order of 20-30-mu-m in width bounded by high density dislocation pile-ups. Higher In(x)Ga(1-x)As compositions resulted in large densities of threading dislocations with Burgers vectors perpendicular to the growth direction, particularly for step-composition graded layers. We attribute this behavior to roughening of the growth interface.